The present invention relates generally to an apparatus and method for measuring airflow and particulate matter, and more particularly to a rotating test port assembly for measuring air flow and particulate matter in conduits.
The measurement of air flow and particulate matter in a conduit, such as piping, is of great importance to facilities such as power plants where environmental and operational efficiency are of concern. Currently, power plants use a manual measurement process to determine the air flow and the amount of particulate matter contained therein flowing through a conduit. This is done by inserting a test probe device through one or more test ports. The test ports, typically two to four, are welded directly to the conduit to allow the probe to be inserted into a stream of air and particulate matter flowing through the conduit. Typically, a standard ball valve is connected to each of the test ports to allow a user controlled access to the stream. When access is desired, the ball valve is opened and the test probe is inserted therethrough. When testing is finished, the test probe is removed, and the ball valve is closed to prevent the stream from exiting the conduit through the test port.
However, the current measurement process has limitations and can often result in erroneous measurements because the probe only traverses a straight line and portions of the flow area are not measured. Since portions of the flow area are not measured, these portions are assumed for calculating the true flow rate of air in the conduit, thereby resulting in errors. If a two-phase flow of air and particulate matter is being measured, both the air velocity and the particulate flow measurement are affected resulting in degradation of these assumptions and causing even greater errors. Through testing, it has been found that the error in particulate matter measurement may be as high as thirty-five percent of the true flow rate.
One way to combat these errors is to increase the number of test ports on the conduit; however, there are limitations to the number of test ports that can be installed due to the size of the conduit, the material of the conduit, and the service the conduit is being used in. For example, conduits used in corrosive environments may have ceramic linings which limit the number of test ports that can be installed.
Another solution used to reduce measurement errors is to use an articulated test probe that allows a tester to take a measurement in a pattern other than a straight line and, thus cover more of the cross sectional area of the conduit. However, these probes have limitations that affect their accuracy and that cannot easily be corrected or even determined. For example, one of the more common articulated probes has multiple extraction nozzles that draw in particulate matter simultaneously. However, in certain conduit configurations and flow conditions the multiple nozzles may not sample equally. Also, because these probes have moving parts and seals, there is potential for leakage in the sample lines that can adversely affect the measurements. In some instances, the articulated probes become jammed inside the conduit which makes their retrieval from the sampling line difficult. In other instances, the articulated probes, which have a much more complex internal flow path, may become plugged because of moisture content in the sampling stream therefore voiding the measurement.